The present invention relates to grinding wheels and, in particular, to improved molding apparatus that includes a mold liner for efficiently and uniformly forming the wheels prior to curing. The assembly also permits thermal curing the wheels within the mold liner to avoid extraneous handling operations.
Abrasive grinding wheels have long been used in the metal working industry to abrade and cut metal. Grinding wheels of various size, shape, thickness and compositions have been developed to accommodate a vast number of necessary grinding operations. One type of grinding wheel, known as a "cup wheel" is configured in the shape of a cup and has a recessed center depression which is axially aligned to a threaded arbor at the longitudinal center of the wheel. A sidewall surface tapers outwardly from an end surface which contains the arbor. The arbor mounts to a motorized spindle of the grinder.
Even though constructed in large volume, such wheels have traditionally and continue to be hand cast. That is, each wheel is molded through several hand operations to a compacted "green state". The green wheels, in turn, are removed from a forming mold, hand loaded and packed in sand curing trays, prior to being subjected to a programmed curing cycle in an appropriate curing furnace.
Difficulties encountered using known molding techniques arise through inconsistencies in wheel density that occur during placement of the nub which defines the center recess. Another, more critical, problem arises from misalignment of the arbor at a bottom mold plate due to dirt or sand that might exist beneath the arbor during either molding or curing. Misalignment can cause the wheel to oscillate, wobble and vibrate dangerously at speed, unless the grinding surface is trued to the arbor. Alternatively, the wheel must be discarded.
The molding apparatus of the present invention was developed to overcome the foregoing problems and others and provide an improved molding process having fewer hand operations that are less dependant on the worker. A mold liner and spring biased positioning pin were particularly developed to assure constant wheel density and arbor alignment.
The liners permit molding wheels which are not susceptible to the presence of dirt or sand beneath the arbor; which cure in approximately 30 to 36 hours versus 48 hours for conventionally molded, sand cured wheels; which can be immediately removed from the liners after curing, without requiring a cooling period; which do not require the removal of sand residue from the grinding surface; and which for metal backed wheels don't require the separate placement of paper barriers to prevent mixture materials from leaking through the backing piece during molding.
The positioning pin avoids inconsistencies in initial placement which can arise from placement of the nub by the molding operator. Such inconsistencies can lead to wheels of varying density in the region of the arbor.